Fig 1.
Map of the study site showing the station sampled.
Generated using Ocean Data View software (after Schlitzer [98]).
Table 1.
This analysis tests differences in quantitative taxonomic composition of gelatinous zooplankton assemblage considering depth stratum (with three levels), day period (two levels, diurnal and nocturnal), and sample replicate (three levels) as factors. Differences are considered significant if P and MC (P) <0.01 (in bold). df = degrees of freedom; SS = sum of squares; MS = mean squares; P = probability associated with the Pseudo F statistic; MC (P) = probability associated with the Monte Carlo randomization procedure.
Fig 2.
Vertical profiles of physical parameters of the water column.
Temperature and salinity data were collected with a CTD/S4 (InterOcean) regularly throughout October 16 and 17, 2007 off South Brazilian Bight. Shadows indicate nocturnal periods. In the temperature panel the isolines are of 1°C, in the salinity and sigma-t panels the isolines are 0.5.
Fig 3.
Summary of the vertical profiles of chlorophyll-a (a) and light levels (b).
Dotted horizontal lines indicate the variation in the euphotic zone (1% of light level). PAR = photosynthetically active radiation.
Fig 4.
Hierarchical cluster of the samples.
Cluster (group average mode) was generated using a Bray-Curtis similarity matrix after abundance data was transformed by log (x+1). Samples represent a mean of three replicate and are labeled according to the period of the day. The symbols indicate the different depth strata sampled according to the legend (UML = upper mixed layer; DCM = deep chlorophyll-a maximum layer; BL = bottom layer). The numbers in parenthesis indicate the first (1) or second (2) day sampled. A, B, C are the groups formed in the analysis with >40% of similarity and O = outliers.
Fig 5.
Vertical distribution of gelatinous zooplankton species richness and total abundance.
Shadows indicate nocturnal periods. Values are shown as the average ± standard deviation.
Table 2.
Summary of gelatinous zooplankton diel vertical distribution on South Brazilian Bight.
Species richness and abundance (ind. or col. 10 m-3) of total and main gelatinous taxa/developmental stage is shown as average ± standard error (n = 12 on each case). An analysis of variance (ANOVA) was performed to test the effect of depth stratum (UML = upper mixed layer, 0–40 m; DCM = deep chlorophyll maximum layer, 40–70 m; BL = bottom layer, 70–100 m) on each variable considering diurnal and nocturnal data-sets separately. In case of significant differences (in bold; p<0.05) a t test was used to compare each pair of strata after applying the Bonferroni correction, the results indicated by the superscript letter; strata sharing at least one letter do not differ significantly between each other.
Fig 6.
Vertical distribution of most abundant medusae.
Shadows indicate nocturnal periods. Values are shown as average ± standard deviation. Notice different scales.
Fig 7.
Vertical distribution of most abundant siphonophores.
Shadows indicate nocturnal periods. Values are shown as average ± standard deviation. Notice different scales.
Fig 8.
Vertical distribution of other common siphonophores and the most abundant ctenophore.
Shadows indicate nocturnal periods. Values are shown as average ± standard deviation. Notice different scales.
Fig 9.
Vertical distribution of most abundant thaliaceans.
Shadows indicate nocturnal periods. Values are shown as average ± standard deviation. Notice different scales.
Fig 10.
Summary of the diurnal and nocturnal vertical distribution of gelatinous zooplankton from South Brazilian Bight.
Data is presented as percentage of the total abundance (ind. 10 m-3) found in the water column during diurnal (open bars) and nocturnal (black bars) samplings combining both days. e = eudoxids, p = polygastrics, g = gonozooids, p = phorozooids, n = old nurses, whenever not indicated developmental stages were pooled due to similar distribution.
Fig 11.
Vertical distribution of copepods and other zooplankton groups.
Abundances were estimated from the first series of the triplicate samples and were based on counts of whole samples (larvaceans and chaetognaths) or 1/4 to 1/32 aliquots (all other taxa). Shadows indicate nocturnal periods. Notice different scales.
Fig 12.
Ordination diagrams of the Redundancy Analysis.
Graphs show the relationship of species/developmental stages and biotic and abiotic explanatory variables during diurnal (a) and nocturnal (b) periods showing the first and second canonical axes. Species are shown as black continuous vectors and explanatory variables as dotted grey vectors. Samples are shown as circles with colors changing according to the depth strata (see legend) and named according to the first or second day sampled (D1 or D2 respectively) and the time of sampling. The percentage of the species data variation explained by each environmental axis is shown in parentheses. Environmental variables codes: Chl = chlorophyll-a, Cop = copepods, PAR = photosynthetically active radiation, Sal = salinity, Temp = temperature. Species codes: Ae = Abylopsis eschscholtzii, Ah = Aglaura hemistoma, At = Abylopsis tetragona, B = Beroe sp., Cg = Corymorpha gracilis, Co = Cordagalma ordinatum, Db = Diphyes bojani, Dg = Dolioletta gegenbauri, Dn = Doliolum nationalis, Eh = Enneagonum hyalinum, Lt = Liriope tetraphylla, Mk = Muggiaea kochii, Sf = Salpa fusiformis, Td = Thalia democratica. The first letter before the species name refer to the life cycle stage of calicophorans (e = eudoxids, p = polygastrics) and thaliaceans (a = aggregate zooids, f = phorozooids, g = gonozooids, n = old nurses, s = solitary zooids). UML = upper mixed layer; DCM = deep chlorophyll-a maximum layer; BL = bottom layer.
Table 3.
Summary of the Redundancy Analysis.
This analysis was performed between the 23 dominant gelatinous zooplankton taxa/developmental stage and the selected explanatory variables during diurnal and nocturnal periods.